New light on the scaling of metabolic rate with the size of algae

The scaling of metabolic rate with the size of algae has been discussed and researched at length. The observation that algae usually have exponents b in the equation R = a(.)W(-b) (where R is the specific growth rate, W is the organism [cell] biomass, and a and b are constants) equal to or higher than the value of -0.25 for many other organisms is generally related to resource-saturated (maximal) values of R. Recent work has shown that the exponent b for light-limited growth is more negative than -0.25. This was predicted from considerations of the package effect in photon absorption, as modulated by the volume-specific pigment content of the cells, and the photosynthetic unit size. Further work is needed to extrapolate these findings to fluctuating light environments. This minireview puts the recent work into a broader context and suggests how further work could quantify the roles of optical thickness and of spatial and temporal variations in the radiation field in determining metabolic rates.